Boring bars that are used with numerically controlled tape machines are of the detachable nature having an insert holding portion on one end and a collar type attachment on the other such that the boring bars may be attached to turrets and the like and used upon a tape controlled cutting machine. The tape controlled cutting machine usually has a referenced datum dimension when measured from some control point on the tape controlled machine spindle to the end point where the cutting insert will perform upon the workpiece.
When using boring bars, usually, the head of the boring bar, itself, is a replaceable item such that different cutting configurations and cutting tools may be interchanged on the boring bar to provide the desired end result on the workpiece. Besides the head being interchangeable, the boring bars also use cemented hard metal carbide inserts which are, themselves, indexable and, also, interchangeable such that inserts, themselves, may be changed at some point during the cutting operation when the cutting insert becomes dull.
It is desirable that, if either the head of the boring bar, the insert on the boring bar or the tooling configuration on the end of the boring bar is changed, that the referenced datum dimension referred to above can be compensated for on the boring bar tool, itself, rather than reprogramming the dimension that has been set on the tape.
It is, therefore, desirable when constructing a boring bar having an axially adjustable feature on it to insure that the boring bar as a whole remains as rigid as possible while, also, trying to insure that the construction of the boring bar is economically feasible.
Other constructions of such axial adjustment mechanisms are described and claimed in U.S. Pat. application Ser. No. 675,322, filed Apr. 9, 1976, assigned to Kennametal Inc., and U.S. Pat. No. 3,911,542, which is also assigned to Kennametal Inc.
It is an object of the present invention to provide a shank for a boring bar whose axial length is adjustable and yet is of a rigid and economical construction.